i've said this a million times in the past but,
i think the issue is that people take being "fat" as an entire identity
it's not who you are. it's not who you're "born to be".
it's just something that accumulates on ur body when u have an excess of calories and not enough exercise.
it's something u can control, unless you have some sort of condition which prevents you from doing so (which is rare).
whenever you're ready, and are serious enough, you can change it.
period. it's pretty simple.
people have to stop making it such an "identity" topic and think logically - address it like the numbers game it is.
what she probably sees in the mirror is a need for her to change.
it's possible that she may be having the same moment mo'nique had when she decided to switch things up
all of that "woo! large and in charge! lovin it! dis who i iz! fuck u skinny bitches!" mess may be wearing off a bit and i can see her eventually buckling down and taking her health seriously.
vanity is the least of ur worries with this type of thing so i hope those around her who love her, encourage her to do what's best for her.